1. Field of the Invention
The present invention relates generally to gas turbine engine, and more specifically for an apparatus and process for measuring creep of a rotor shaft of an industrial gas turbine engine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by increasing the compression ratio. Increases in compression ratio in modern IGT engines cause an increase in the compressor exhaust temperatures, which for some engines can translate into increased creep deformation of the rotor at the later compressor stages.
Some of the current state of the art IGT engines have a monolithic rotor shaft instead of a number of smaller rotor disks bolted together to form the entire rotor for the engine. A monolithic rotor shaft is one single piece rotor shaft for the entire engine. One major problem with an engine having a monolithic rotor is with creep. Creep occurs due to high centrifugal forces from rotation and is exacerbated by high temperatures. In the case of a rotor, creep deformation will cause permanent radial growths that tend to force the material to grow outward. If the rotor suffers from excessive creep, cracks will develop that can eventually result in the catastrophic damage to the rotor and therefore to the engine. An OEM of these monolithic rotor engines will typically issue a conservative maximum time allowance for safe usage for the rotor in which the older rotor must be replaced before and creep damage becomes significant. Currently there is no commercially available way of measuring the remaining creep capability of a rotor. This in combination with the fact that safe operation rotor life estimates tend to be developed for worse case conditions, and in a very conservative manners, results in situations where an older rotor that would still have remaining safe service life would potentially be replaced, at a substantial cost to the IGT engine user.